Vol 53, No 3 (2017)

We present a brief review of research and design work aimed at producing tungsten-containing hard alloys for various applications. We examine the feasibility and prospects of using a chemical metallurgy method and self-propagating high-temperature synthesis (SHS) for the preparation of submicron and nanoscale hard-alloy powders as a key component of highly efficient state-of-the-art materials and products. Particular examples are presented of the use of submicron and nanoscale powders for the preparation of TVS tungsten-based heavy metallic alloys and VK tungsten carbide hard alloys for various applications. Their application fields are discussed and their properties are compared to those of their analogs produced by conventional powder metallurgy methods. Using the SHS of tungsten carbide as an example, we demonstrate a particular path from research to commercialization (from the discovery of SHS processes to commercialscale production) of key modern engineering materials: tungsten-based heavy alloys and tungsten carbidebased hard alloys.

Cadmium sulfide was prepared by colloidal synthesis in methyl methacrylate (MMA). Europium and terbium salts were added to the colloidal solutions. Using MMA radical polymerization, we synthesized PMMA/CdS:Eu(III), PMMA/CdS:Tb(III), and PMMA/CdS:Eu(III):Tb(III) luminescent composites. Their luminescence is due to defects in the CdS crystals and the ⁵D_о → 7Fj and ⁵D₄ → ⁷F_j electronic transitions of the Eu³⁺ and Tb³⁺ ions, respectively. It depends on the composition of the materials, complexation on the surface of the colloidal particles, heat treatment time during synthesis, excitation wavelength, and other factors.

We have studied the combustion of titanium in nitrogen in the presence of ammonium chloride. It has been shown that the use of NH₄Cl in the self-propagating high-temperature synthesis of TiN considerably reduces the combustion temperature, prevents sintering of the synthesized titanium nitride particles, and increases their specific surface area. The synthesis products have the form of nanostructured titanium nitride particles which reproduce the shape of the starting titanium particles but consist of equiaxed titanium nitride grains ranging in size from 50 to 500 nm. We have obtained nanostructured titanium nitride powders ranging in specific surface area up to 80 m²/g.

This paper examines the physicochemical properties and microstructure of brushite calcium phosphate cements possessing strength acceptable for application in surgery (15–20 MPa) and ensuring an optimal acidity (pH 6.5–7.5) of solutions in contact with them. Holding in a physiological saline produces significant changes in the microstructure of the cement relative to that before immersion in the solution: it causes a transformation of the most soluble components into platelike hydroxyapatite crystals.

BaI₂:Eu²⁺,Eu³⁺ powders have been prepared by heat-treating BaCO₃:Eu³⁺ precursor powders of various morphologies in an iodinating agent atmosphere and their structural properties, morphology, optical absorption, and luminescence have been studied. The results demonstrate that the powders thus prepared consist of a mixture of crystalline hydrates of various compositions, dominated by BaI₂ ∙ 2Н₂О (sp. gr. C2/c), and that the Eu²⁺: Eu³⁺ ratio in the powders is determined by the morphology of the precursor.

We have prepared ceramic samples of (1–x)Ba(Ti_1–yZr_y)O₃ ∙ xPbTiO₃, (у = 0–0.10, x = 0–0.67) ferroelectric perovskite solid solutions and characterized them by X-ray diffraction and dielectric and pyroelectric measurements. The composition dependences of the unit-cell parameters for the solid solutions have been obtained; their Curie temperature T_C, relative dielectric permittivity ε, and loss tangent tan δ have been measured at temperatures from 100 to 700 K and frequencies from 25 Hz to 1 MHz; and characteristics of their dielectric hysteresis loops and pyroelectric effect have been assessed. With increasing PbTiO₃ content, the T_C of the samples increases from 400 (x = 0) to 670 K (x = 0.67), the temperatures of their low-temperature phase transitions decrease (to the point that they disappear for x > 0.15), and ε(T = 296 K) decreases at x > 0.1.

The coprecipitation of calcium hydroxyapatite (HA) (Ca₁₀(PO₄)₆(OH)₃) and silk fibroin (SF) from an aqueous solution in the Ca(NO₃)₂–(NH₄)₂HPO₄–NH₃–H₂O–SF system has been used to synthesize HA/SF organomineral composites based on nanocrystalline HA, containing 2, 5, and 10 wt % SF. The synthesis products were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, scanning electron microscopy, and electron spectroscopy for chemical analysis.